Re: Indexes on NULL's and order by ... limit N queries

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От Alvaro Herrera
Тема Re: Indexes on NULL's and order by ... limit N queries
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Msg-id 20081201204144.GL4459@alvh.no-ip.org
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Ответ на Re: Indexes on NULL's and order by ... limit N queries  (Maxim Boguk <mboguk@masterhost.ru>)
Ответы Re: Indexes on NULL's and order by ... limit N queries  (Maxim Boguk <mboguk@masterhost.ru>)
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Maxim Boguk wrote:
> Sorry with all my respect to you, you look like wrong.

The difference is that the plan with -1 does not need to sort the
output, because it comes sorted out of the index; so the execution can
be stopped as soon as 5 tuples have come out.  With NULL, that can't be
done.

--
Alvaro Herrera                                http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support

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